The long-term goal of our work is to understand the interactions of sperm with the female reproductive tract that are required for fertilization. Infertility affects about 7% of married couples in the US and the success rate of artificial insemination in the cattle industry has been dropping over the past several years. Sexually transmitted diseases (STDs) such as trichomoniasis are a major problem for both humans and cattle. Lastly, safer forms of contraception are needed for humans. Understanding the processes of sperm and pathogen migration through the female reproductive tract could enable the development of new methods for diagnosing and treating infertility, protecting against STDs, and preventing unwanted pregnancies. We are proposing a unique two-pronged approach to identify biophysical and biochemical factors that promote sperm migration to the egg but also inhibit the rise of STD pathogens, particularly those causing trichomoniasis. For this project, the bovine model will not only provide useful information to the cattle industry but also to human medicine, because biophysical and biochemical aspects of the migration of bull sperm through the cervix, uterotubal junction, and oviduct are quite similar to those of humans. Aim 1 is to identify roles of physical factors that guide sperm migration in the cervix and uterotubal junction. To achieve this, we will carry out the following subaims. 1A. Develop a microfluidic model that mimics three parameters of the physical environments of the passages in the cervix and uterotubal junction: the microchannels in the walls of the main central channel, fluid flow, and fluid viscoelasticity. 1B. Test the hypothesis that microchannels in the walls of the cervix and uterotubal junction assist sperm in moving upstream in the presence of a flow. As part of the investigation, we will explore the roles of fluid viscoelasticity in facilitating sperm migration against the flow. 1C. Test the hypothesis that physical parameters facilitate the entry of sperm into the microchannels in preference to entry of pathogens, particularly Tritrichomonas foetus. Aim 2 is to elucidate how the molecules involved in binding sperm to oviductal epithelium regulate sperm migration up the oviduct. We will test the hypothesis that loss and modification of Binder of Sperm proteins (BSPs) play crucial roles in releasing sperm from the oviductal storage reservoir toward the upper oviduct. Binding of bull sperm to oviductal epithelium is mediated by 3 BSPs on sperm, which interact with 4 annexin proteins (ANXAs) on the oviductal epithelium. Binding is reduced by capacitation, so we propose to test its effects on BSPs and on release of sperm from oviductal epithelium, as well as the role that the interactions of BSPs with ANXAs could play in guiding sperm to the egg.